The studies proposed here are designed to enhance our understanding of the signalling pathways that lead to cancer. Cancer is a disease caused by mutations in a group of genes known as proto- oncogenes. One of the most commonly mutated proto-oncogenes is the ras oncogene. This project will study proteins that interact with the ras gene homologs of the yeast Saccharomyces cerevisiae. This yeast is the only organism which ras has a well defined function, the cAMP signalling pathway. Yeast, and also mammalian ras both activate yeast adenylyl cyclase. Adenylyl cyclase in S. cerevisiae contains at least two subunits, a 200 kDa catalytic subunit and a 70 kDa cyclase associated protein, CAP. CAP is bifunctional, serving as a positive regulator of cAMP levels and mediating a non-cAMP signal as well. The details of how CAP and adenylyl cyclase interact will be explored through biochemical mapping studies. The properties of adenylyl cyclase in its CAP-bound and CAP-free forms will be studied in enzyme kinetic experiments, paying particular attention to any influence CAP may have on activation of adenylyl cyclase by RAS. The non-cAMP function of CAP will be studied by identifying and cloning suppressors of CAP induced phenotypes. Finally, mammalian cDNA libraries will be screened using yeast genetic assays to identify mammalian suppressors of the CAP non-cAMP function. Together these studies will enhance our understanding of how ras interacts with its only known effector, S. cerevisiae adenylyl cyclase, and then test the extent to which some of these interactions are conserved in mammals.